1. Field of the Invention
The present invention relates to a transmission line in which signal conductors that transmit different high-frequency signals are located close to each other.
2. Description of the Related Art
Various types of transmission lines that transmit high-frequency signals have been proposed. For example, a transmission line described in Japanese Patent No. 4962660 has a stripline structure. The transmission line described in Japanese Patent No. 4962660 includes a long dielectric body, a signal conductor, and first and second ground conductors. The signal conductor is disposed in the middle of the dielectric body in the thickness direction. The first ground conductor and the second ground conductor are arranged, with the signal conductor sandwiched therebetween, in the thickness direction of the dielectric body. The first ground conductor and the second ground conductor are connected to each other by a plurality of via hole conductors (interlayer connection conductors) arranged along the signal conductor. With this configuration, a transmission line having a stripline structure in which the signal conductor is sandwiched between the first and second ground conductors is obtained.
When a plurality of transmission lines, each having a configuration such as that described in Japanese Patent No. 4962660, are arranged close to each other in a communication device, a plurality of signal conductors may be arranged in a single dielectric body. In this case, the plurality of signal conductors may be spaced in a direction orthogonal to the thickness direction of the dielectric body.
That is, the transmission lines each having the structure described in Japanese Patent No. 4962660 may be arranged in a direction orthogonal to the thickness direction of the dielectric body.
As the sizes of electronic devices including a transmission line mounted thereon become smaller, the demand for reducing the size of the transmission line increases. At the same time, when adjacent signal conductors are close to each other, the signal conductors are coupled to each other. For example, when the configuration described above is used, narrowing the width of the transmission line leads to a reduced distance between the signal conductors, which are thus prone to being coupled to each other. As a result, the level of isolation between transmission lines including the signal conductors is reduced.